The hallways are sparse, painted white. Some are seemingly endless stretches of gray, concrete floor.

There are few hints that the Mesa fortress you have stepped into belongs to Apple Inc., the technology behemoth based in Cupertino, California.

The Arizona Republic took a rare tour inside Apple's 1.3 million-square-foot data center on the corner of Signal Butte and Elliot roads. The company, known for its secrecy, would not share many specifics about what happens inside the facilityfilled with servers, citing security concerns.

In a room, dubbed the "global data command" center, a handful of employees, working in 10-hour shifts, monitor Apple operations data. That could include data from applications such as iMessage, Siri and iCloud.

Five other Apple data centers from California to North Carolina run similar operations. Apple announced in 2015 that it would open operations in Arizona and has employed about 150 people at the Mesa facility since 2016.

The facility completed its latest addition, which includes severalmore halls of servers, in April.

Inside look at a server room at the Apple Data Center in Mesa on Aug. 14, 2018.(Photo: Tom Tingle/The Republic)

Gov. Doug Ducey is stopping at the data center on Wednesday to commemorate the company's latest addition. The plant was a key jobs victory for Ducey, who is seeking reelection this fall, during his first year in office.

The Apple plant originally was built by Tempe-based First Solar Inc. with plans to employ about 600 workers, but was never fully occupied. Next came GT Advanced Technologies Inc., a sapphire-glass supplier to Apple. That company filed for bankruptcy and vacated the building in 2014.

Apple has been reconfiguring the plant for the last several years.

The facility is not recognizable as Apple's from the outside, surrounded by thick, dark walls draped in vines. A guard patrols the entrance to the parking lot.

Server halls contain dozens and dozens of rows of large, humming electronics. Booming fans sit above the servers in an effort to cool the technology.